The present invention relates to a part-mounting system (a part-mounting line), for mounting an electronic part onto a board, comprising a plurality of part-mounting devices, and a method of mounting parts.
A part-mounting line for mounting an electronic part onto a board is formed by linking various part-mounting devices such as a screen-printing device, a part-mounting device and the like. In such a part-mounting line, since the respective part-mounting devices are linked to each other, the following point is taken into consideration: A cycle time of the part-mounting line (a total processing time required by the line) is desirably minimized in order to maximize productivity, and cycle times for the respective mounting devices (a process time required by each device, and hereinafter referred to as a xe2x80x9ctact timexe2x80x9d) are prepared considering balances between respective devices.
In general, a tact time of respective devices is often inconsistent with quality of the work in a corresponding device. For instance, in a screen printing device for printing cream solder onto a board, when a printing speed is raised, print defects tend to increase. In a part-mounting device for mounting a part onto a board, when a mounting speed is set at a higher speed, the number of mounting-errors increases. Therefore, when the cycle time of the part-mounting line is prepared, the trade-off between productivity and quality is seriously taken into consideration before the most reasonable cycle time is set.
However, even if the most reasonable cycle time is used, the following problems still occur in an actual production line: Each of the mounting devices sometimes pauses for supplementing the shortage of parts, or due to unexpected defects. These happenings delay the tact time. In such a case, an operation is halted or production is delayed at that mounting device, and yet, this delay inevitably influences other mounting devices in the same line.
In the mounting devices on the downstream side of that problem-happened mounting device, boards are not supplied on schedule based on the tact time. As a result, waiting time is produced, and the device halts its operation during the waiting time. On the upstream side of that problem-happened mounting-device, even if the production is kept going on schedule based on the tact time, boards are piled up just before the problem-happened mounting device. As a result, when a number of boards piled up exceeds a given number, the production is halted, and the waiting time is produced also. Thus the volume produced in the mounting line does not reach the expected volume corresponding to the cycle time prepared before the production starts, which means that the productivity of the line lowers from the expected level. In other words, this situation produces the same result as when slower tact times of each mounting device than those in this case discussed above are used.
When a quality level of the board produced in the delayed tact-time situation is considered, we may get the following result: Each board has undergone the respective mounting devices at the operation speed based on the tact time prepared before the production started, thus each of the boards has obtained a quality level lower than the quality level which would be obtained at a slower tact time. In other words, the mounting-line has produced the boards having the lower quality level than an expected one at a lower productivity than an expected productivity. The expected quality level and productivity are derived from the trade-off between productivity and quality. Thus an opportunity loss has occurred in the production line.
The present invention provides a part-mounting system formed of a plurality of part-mounting devices, for mounting parts on a board, linked to each other in series. The system comprises the following elements:
(a) a tact-time detecting means for detecting a production tact-time of a first part-mounting device;
(b) signal outputting means for outputting a tact-time change signal to a second part-mounting device disposed on upstream and/or downstream side from the first part-mounting device when the production tact-time detected varies beyond a given variation range; and
(c) tact-time setting means for changing a work tact-time of the first part-mounting device after receiving a tact-time change signal supplied from a part-mounting device other than the first part-mounting device.
The present invention provides a first part-mounting device xe2x96xa1 an element of a part-mounting system formed by linking a plurality of part-mounting devices xe2x96xa1 comprises the following elements:
(a) tact-time detecting means for detecting a production tact-time of the first part-mounting device;
(b) signal outputting means for outputting a tact-time change signal to a second part-mounting-device disposed on upstream and/or downstream side from the first part-mounting device when the production tact-time detected varies beyond a given variation range; and
(c) tact-time setting means for changing a work tact-time of the first part-mounting device after receiving a tact-time change signal supplied from any part-mounting device other than the first part-mounting-device.
The present invention provides a method of mounting parts onto a board through linking a plurality of part-mounting devices and having respective devices mount parts on the board. The method comprises the following steps:
(a) detecting a production tact-time of a first part-mounting device;
(b) outputting a tact-time change signal to a second part-mounting device disposed on upstream and/or downstream side from the first part-mounting device when the production tact-time detected varies beyond a given variation range; and
(c) changing a work tact-time of the first part-mounting device after receiving a tact-time change signal supplied from any part-mounting device other than the first part-mounting device.
Another method may include, instead of step (c), a step of changing a work tact-time of the second part-mounting device after the tact-time change signal supplied in step (b) is received.
According to the present invention, if a tact-time of one of part-mounting devices is delayed due to an external disturbance, tact-times of other devices included in a mounting line can accommodate themselves to the change of the tact-time, thereby securing the quality appropriate to those tact-times changed.